The present invention relates to non-hermetic seals. More specifically, the present invention relates to non-hermetic seals used for sealing individually wrapped items of food and to methods and apparatus for forming such non-hermetic seals.
FIG. 1A shows a front view of a portion of a prior art chain 100 of individually wrapped food items. FIGS. 1B and 1C show sectional views of chain 100 taken along lines 1B--1B and 1C--1C, respectively, as shown in FIG. 1A. FIG. 1B additionally shows figuratively an apparatus 101 for forming chain 100.
Chain 100 includes a series of packets 110. Each pair of adjacent packets 110 in chain 100 is separated by a transversal seal area 112. As shown in FIGS. 1A and 1C, a longitudinal seal area 113 also extends along one side of chain 100 in a direction substantially perpendicular to the transversal seal areas 112. As shown in FIGS. 1B and 1C, an item of food 114 (e.g., a slice of cheese) is encased within each packet 110. Each packet is characterized by a length L and a height Hp. Each transversal seal area 112 is characterized by a length L (equal to the length of the packets) and a height Hs. When the food items 114 are cheese slices, typical dimensions for L, Hp, and Hs are 86 mm (millimeters), 85 mm, and 15 mm, respectively.
Apparatuses for forming chain 100 are well known in the art and one example of apparatus 101 (indicated in FIG. 1B) is described in U.S. Pat. No. 3,542,570 (which is assigned to L. D. Schreiber Cheese Company, Inc. and which was invented by Robert G. Bush and Gilbert H. Hannon). Briefly, apparatus 101 is coupled to a source of food 102 and a large roll 103 of flexible wrapping material (e.g., cellophane). Roll 103 feeds a sheet of wrapping material 104 into apparatus 101 and food source, or nozzle, 102 injects food (e.g., viscous cheese) into apparatus 101. Apparatus 101 forms the sheet 104 into a tube as indicated generally in FIG. 1D, which shows a perspective view of a portion of the tube. Apparatus 101 also uses heat or pressure to form longitudinal seat area 113 by pressing overlapping portions of the tube together as indicated in FIG. 1D. Apparatus 101 also presses selected portions of sheet 104 together to form transversal seal areas 112 and thereby forms the sheet 104 into packets 110. For example, as shown in the perspective view of FIG. 1E, apparatus 101 presses portions 126 and 128 of sheet 104 together to form a single transversal seal area 112. Food source 102 injects the food item into the packets 110 as the packets are being formed. The sheet of wrapping material 104 used to form packets 110, seal areas 112, and seal areas 113 is preferably moisture proof and gas proof so the packets 110 can adequately preserve the freshness of the food items 114. Although FIGS. 1A and 1B only show five packets 110 in chain 100, those skilled in the art will appreciate apparatus 101 forms the chain 100 continuously, and the chain 100 can include many more packets 100.
FIG. 1F shows a magnified front view of one of the seal areas 112 shown in FIGS. 1A and 1B. FIG. 1G shows a sectional view of the seal area taken along the line 1G--1G shown in FIG. 1F. For convenience of illustration, the longitudinal seal area 113 is not shown in FIG. 1F. As shown, each seal area 112 includes eight parallel sealed strips 122 and seven unsealed strips 124, with an unsealed strip 124 separating each pair of adjacent sealed strips 122. Each of the sealed strips 122 and unsealed strips 124 extends across the full length L of the seal area 112. The sealed strips are typically formed by pressing portions of the sheet 104 of wrapping material tightly together and by locally heating the wrapping material (e.g, a strip of portion 126 and a strip of portion 128, as shown in FIG. 1E, would be pressed together to form a single sealed strip 122). At the sealed strips 122, the portions of wrapping material are permanently bonded together, and the sealed strips can not be "unsealed" without tearing or otherwise damaging the wrapping material. The collection of sealed strips 122 in seal area 112 forms a tight hermetic seal between the two adjacent packets 110 and thereby protects the freshness of the food items 114.
The unsealed strips 124 are formed by adjacent portions of the sheet 104 of wrapping material that have not been sealed together. As shown in FIG. 1G, a small amount of trapped air may separate the two portions of wrapping material at the unsealed strips 124. However, even if the trapped air were eliminated permitting the portions of wrapping material to contact one another at the unsealed strips 124, the portions of wrapping material would not be not bonded together at the unsealed strips 124. As shown in FIG. 1G, the unsealed strip 124a is formed by a portion 130 of sheet 104 (shown in FIG. 1B) and by a portion 132 of sheet 104 (shown in FIG. 1B). The portions 130, 132 are not bonded together and are held in place with respect to one another only by the adjacent sealed strips 122. The portions of the sheets used to form each of the unsealed strips are held in place with respect to one another only by the adjacent sealed strips.
In a typical food production process, after chain 100 is formed, the packets 110 are separated from one another (e.g., by slicing the seal areas 112 in half along their length L) and then stacked to form a stack 200 as shown in FIG. 2. Stack 200 is then normally encased in an outer wrapping (not shown), and sold as a collection of individually wrapped food items (e.g., individually wrapped slices of cheese).
FIG. 3A shows a side view of an apparatus 300 for forming seal areas 112. Apparatus 300 would normally be considered a part of apparatus 101 (shown in FIG. 1B). Apparatus 300 includes two wheels 310, and each of the wheels is studded with a set of four cleats 312a, 312b, 312c, and 312d. The chain 100 is threaded between the two wheels 310 and travels downwards as the wheels rotate synchronously in the directions indicated by arrows 314. In the position of apparatus 300 illustrated in FIG. 3A, cleats 312a from both wheels 310 are simultaneously pressing two portions of sheet 104 of wrapping material (between the two packets 110) together to form a seal area 112. The cleats 312 are typically heated so a combination of pressure and heat is used to form the seal areas 112. As the wheels 310 rotate, corresponding cleats from both wheels periodically meet to form one of the seal areas 112. Wheels 310 are disposed so their outer perimeters (in areas without cleats) are separated by a distance at least as large as the width of packet 110, so the packets 110 can pass undisturbed through the wheels 310 as the wheels rotate.
FIG. 3A shows a clamped area 316 at the top of the upper packet 110. Clamped area 316 is typically formed by clamping or squeezing the two sheets wrapping material together tightly enough to temporarily hold the sheets of wrapping material together, but not tightly enough to permanently bond the sheets of wrapping material together. Although clamped area 316 defines (at least temporarily) the shape of packet 110, the food item in the packet 110 is not adequately sealed (so as to preserve freshness) until the clamped area 316 passes through the cleats 312 of sealing apparatus 300 and is thereby turned into a proper seal area 112.
FIGS. 3B, 3C, and 3D show magnified front, side, and perspective views, respectively, of one of the cleats 312 of apparatus 300. As shown, cleat 312 has a generally corrugated appearance and defines eight distinct bearing surface strips 320, with each of the bearing surface strips extending across the entire length L (equal to the length of the seal area 112) of the cleat 312. FIG. 3E shows a magnified side view of two cleats 314 meeting to form a seal area 312. As shown, the bearing surface strips 320 of the two opposing cleats press the wrapping material tightly together to form the eight sealed strips 122 of seal area 112. Although not illustrated, the cleats 314 are generally heated so a combination of heat and pressure are used to form the sealed strips 122.
Although the illustrated cleats provide eight relatively small bearing surface strips 320, it is possible to use cleats 312 that provide only a single relatively large bearing surface. Such a cleat would produce a seal area 112 having only a single sealed strip. However, it is well known that cleats of the form illustrated in FIGS. 3B-3E that provide a plurality of relatively small bearing surface strips produce much tighter, more effective, seal areas 112.
One disadvantage of seal areas 112 of the type shown in FIG. 1F is that they are very difficult to break or open. Customers must typically break or open these seal areas before they can consume the food items 114. Although it is desirable for the seal areas 114 to protect the freshness of the food item, the seal areas should also provide customers relatively easy access to the food items.
It is therefore an object of the present invention to provide seal areas in a chain of food items that (1) adequately protect the freshness of the food items and (2) are relatively easy for customers to open.